This invention relates to a process for converting organic waste material into methane and other useful products such as fertilizer. More specifically, this invention relates to an anaerobic digestion process which is conducted in several zones.
Organic waste such as straw, alcohol stillage, paper, vegetable refuse and animal wastes, i.e., manure, tuna plant wastes and others have long been considered a potential resource for the production of methane gas. Substantial amounts of money and effort have been directed towards providing a practical process for utilization of this resource. Typical methods involve both aerobic and anaerobic degradation of the waste within a complex system.
Most prior art systems involve treating an aqueous suspension of the waste having a solids content of about 10% or greater in a fermentative system which requires heating of at least part of the system. Such systems also typically require intermittent or continuous mixing and frequent periodic maintenance. Recirculation of microbe-rich or activated sludge is often an essential part of the system and operation normally requires nontrivial technological expertise. Initial capital investment to acquire such systems is generally prohibitive.